Lung diseases, including lung cancer and chronic lung diseases such as chronic obstructive pulmonary disease, together account for some 280,000 deaths annually (American Lung Association). Contributing to this mortality is the fact that remediation of all forms of lung disease is hampered by the limited ability of lung to regenerate. Hence, lung tissue that is damaged by degeneration or infection, or lung tissue that is surgically resected, is not functionally replaced in vivo. Currently, the only way to replace lung tissue is to perform lung transplantation, an expensive procedure that is achieves only a 10% survival at 10 years, and one that is hampered by a severe shortage of organs. Over the past 3 years, we have worked to address some fundamental challenges in lung tissue engineering. In order to produce a lung scaffold that has suitable geometry and mechanics for lung regeneration, we have developed technologies to decellularize entire lung tissues. We have shown that these acellular lung matrices retain the gross mechanical properties of the original lung tissues, and provide outstanding support for the adhesion and growth of epithelial and vascular cells. We have developed a novel, biomimetic bioreactor that provides for long-term sterile lung culture, circulation of nutrient medium through the lung vascular compartment, and breathing of nutrient medium into the airway. As a cell source to repopulate the acellular lung matrix, we have utilized syngeneic neonatal rat lung cells, as these cells show significant potential for growth inside the developing lung. We have made substantial and exciting progress in this work, and have shown the feasibility of regenerating many characteristics of lung tissue, but there remain several important issues that must be studied and addressed before the functionality of such lung tissues can be tested in vivo. Most fundamentally, in order to exchange gas, the lung must comprise sufficient alveolar diffusional surface area, must be populated with functional and differentiated epithelial cell subsets at correct anatomic locations in the alveoli and elsewhere, and must be invested with a functional microvasculature that withstands physiological perfusion pressures and does not leak fluid into the alveolar compartment. In this proposal, we will study and refine the lung tissue engineering system in order to address each of these issues and advance the central mission of functional lung regeneration, which is the capacity for effective gas exchange. We hypothesize that the acellular lung matrix, when suitably re-populated with lung epithelium and vascular cells, will support the growth and differentiation of these cells and will produce a tissue that is effective for gas exchange, based upon in vitro measurements.